Set to take place in the same world as The Legend of Zelda: A Link to the Past, I like how they went with a similar title, Link being a link to something. With the title being "Between Worlds". it's safe to assume that the worlds are the normal game world and the wall painting world and Link is the link between them since he can travel to both world freely. As expected, the whole wall painting mechanic will be used to traverse areas around the world and solve puzzles in dungeons. Your typical Zelda fare.
A Link to the Past was the very first Zelda game that I really played. Technically the first one I played was the very first The Legend of Zelda on the NES but I really got into A Link to the Past when I borrowed a friend's copy on the GBA. And seeing that world in full 3D is just amazing. The top down view and with more emphasis on vertical travel is perfect for the 3DS' 3D slider. A lot of A Link to the Past items also make a return, such as the hammer (which is now orange) and fire rod. I also like how they gave Link his more classic colors such as the gold trim around his hat and the brown undershirt.
The dark triforce symbol on the title screen would lead me to believe that we might also see the return of the Dark World. The title also doesn't specify exactly how many worlds Link will be able to travel to and I wouldn't be surprised if the Dark World was like a surprise twist or something or that notion.
If you've been waiting for a reason to pick up a 3DS, this looks about as good a reason as any. Oh and Project x Zone is also a pretty good reason.